diff --git a/src/compile.zig b/src/compile.zig
index 48eaeb0..5f8a26c 100644
--- a/src/compile.zig
+++ b/src/compile.zig
@@ -46,10 +46,9 @@ const Parser = struct {
     scanner: *Scanner,
     had_error: bool,
     panic_mode: bool,
-    chunk: *Chunk,
     vm: *VM,
 
-    fn new(vm: *VM, compiler: *Compiler, scanner: *Scanner, chunk: *Chunk) Parser {
+    fn new(vm: *VM, compiler: *Compiler, scanner: *Scanner) Parser {
         return Parser{
             .compiler = compiler,
             .current = null,
@@ -57,13 +56,12 @@ const Parser = struct {
             .scanner = scanner,
             .had_error = false,
             .panic_mode = false,
-            .chunk = chunk,
             .vm = vm,
         };
     }
 
     inline fn current_chunk(self: *Parser) *Chunk {
-        return self.chunk;
+        return &self.compiler.function.chunk;
     }
 
     fn advance(self: *Parser) void {
@@ -137,11 +135,14 @@ const Parser = struct {
         try self.emit_byte(@intFromEnum(OpCode.OP_RETURN));
     }
 
-    fn end_parser(self: *Parser) !void {
-        if (!self.had_error and self.vm.has_tracing()) {
+    fn end_parser(self: *Parser) !*Obj.Function {
+        if (!self.had_error and constants.DEBUG_PRINT_CODE) {
             self.current_chunk().dissassemble("code");
         }
+
         try self.emit_return();
+
+        return self.compiler.function;
     }
 
     fn number(self: *Parser, can_assign: bool) ParsingError!void {
@@ -702,17 +703,41 @@ const Parser = struct {
     }
 };
 
+const FunctionType = enum {
+    Function,
+    Script,
+};
+
 const Compiler = struct {
+    function: *Obj.Function,
+    function_type: FunctionType,
+
     locals: [constants.UINT8_COUNT]Local,
     local_count: usize,
     scope_depth: usize,
 
-    fn new() Compiler {
-        return Compiler{
+    fn new(allocator: std.mem.Allocator, function_type: FunctionType) Compiler {
+        const obj_function = Obj.Function.new(allocator);
+
+        var compiler = Compiler{
             .locals = undefined,
             .local_count = 0,
             .scope_depth = 0,
+            .function = obj_function,
+            .function_type = function_type,
         };
+
+        compiler.locals[0].depth = 0;
+        compiler.locals[0].name = Token{
+            .token_type = TokenType.EOF,
+            .start = "",
+            .length = 0,
+            .line = 0,
+        };
+
+        compiler.local_count += 1;
+
+        return compiler;
     }
 };
 
@@ -721,13 +746,11 @@ const Local = struct {
     depth: ?usize,
 };
 
-pub fn compile(allocator: Allocator, vm: *VM, contents: []const u8, chunk: *Chunk) !bool {
-    _ = allocator;
-
-    var compiler = Compiler.new();
+pub fn compile(allocator: Allocator, vm: *VM, contents: []const u8) !?*Obj.Function {
+    var compiler = Compiler.new(allocator, FunctionType.Script);
 
     var scanner = Scanner.init(contents);
-    var parser = Parser.new(vm, &compiler, &scanner, chunk);
+    var parser = Parser.new(vm, &compiler, &scanner);
 
     parser.advance();
 
@@ -735,7 +758,11 @@ pub fn compile(allocator: Allocator, vm: *VM, contents: []const u8, chunk: *Chun
         try parser.declaration();
     }
 
-    try parser.end_parser();
+    const function = try parser.end_parser();
 
-    return !parser.had_error;
+    if (!parser.had_error) {
+        return function;
+    } else {
+        return null;
+    }
 }
diff --git a/src/constant.zig b/src/constant.zig
index d0279d8..68a7740 100644
--- a/src/constant.zig
+++ b/src/constant.zig
@@ -7,4 +7,10 @@ pub const UINT16_MAX = std.math.maxInt(u16);
 
 pub const UINT8_COUNT = UINT8_MAX + 1;
 
-pub const STACK_MAX = 256;
+pub const FRAMES_MAX = 64;
+pub const STACK_MAX = (FRAMES_MAX * UINT8_MAX);
+
+pub const DEBUG_PRINT_CODE = true;
+pub const DEBUG_TRACE_EXECUTION = true;
+pub const DEBUG_PRINT_INTERNAL_STRINGS = false;
+pub const DEBUG_PRINT_GLOBALS = false;
diff --git a/src/main.zig b/src/main.zig
index 945ec7d..e919faa 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -2,6 +2,8 @@ const std = @import("std");
 const debug = std.debug;
 const Allocator = std.mem.Allocator;
 
+const constants = @import("./constant.zig");
+
 const Chunk = @import("./chunk.zig").Chunk;
 const OpCode = @import("./opcode.zig").OpCode;
 const VM = @import("./vm.zig").VM;
@@ -17,7 +19,7 @@ pub fn repl(allocator: Allocator, vm: *VM) !void {
     const stdout = std.io.getStdOut().writer();
 
     while (true) {
-        if (vm.has_tracing()) {
+        if (constants.DEBUG_PRINT_GLOBALS) {
             vm.globals.dump();
         }
 
@@ -63,12 +65,6 @@ pub fn main() !void {
     var vm = VM.new(allocator);
     defer vm.free();
 
-    var env = try std.process.getEnvMap(allocator);
-    defer env.deinit();
-    if (env.get("TRACE") != null) {
-        vm.set_trace(true);
-    }
-
     if (args.len == 1) {
         try repl(allocator, &vm);
     } else if (args.len == 2) {
diff --git a/src/object.zig b/src/object.zig
index 0192d2d..38e8297 100644
--- a/src/object.zig
+++ b/src/object.zig
@@ -45,8 +45,8 @@ pub const Obj = struct {
     pub const Function = struct {
         obj: Obj,
         arity: usize,
-        chunk: *Chunk,
-        name: *Obj.String,
+        chunk: Chunk,
+        name: ?*Obj.String,
 
         pub fn new(allocator: std.mem.Allocator) *Function {
             const obj = Obj{
@@ -58,6 +58,7 @@ pub const Obj = struct {
             function_obj.obj = obj;
             function_obj.arity = 0;
             function_obj.chunk = Chunk.new(allocator);
+            function_obj.name = null;
 
             return function_obj;
         }
@@ -89,7 +90,11 @@ pub const Obj = struct {
             },
             ObjType.Function => {
                 const obj = self.as_function();
-                debug.print("<fn {s}>", .{obj.name.chars});
+                if (obj.name == null) {
+                    debug.print("<script>", .{});
+                } else {
+                    debug.print("<fn {s}>", .{obj.name.?.chars});
+                }
             },
         }
     }
diff --git a/src/vm.zig b/src/vm.zig
index d1d510e..e187449 100644
--- a/src/vm.zig
+++ b/src/vm.zig
@@ -13,8 +13,6 @@ const Table = @import("./table.zig").Table;
 const compile = @import("./compile.zig").compile;
 const compute_hash = @import("./utils.zig").compute_hash;
 
-const DEBUG_TRACE_EXECUTION = @import("./main.zig").DEBUG_TRACE_EXECUTION;
-
 const print_value = @import("./values.zig").print_value;
 
 pub const InterpretResult = enum {
@@ -23,10 +21,15 @@ pub const InterpretResult = enum {
     RUNTIME_ERROR,
 };
 
+pub const CallFrame = struct {
+    function: *Obj.Function,
+    ip: usize,
+    // pointer to stack index provided to this frame
+    slots_idx: usize,
+};
+
 pub const VM = struct {
     allocator: Allocator,
-    chunk: ?*Chunk,
-    ip: ?usize,
     stack: [constants.STACK_MAX]Value,
     stack_top: usize,
     // Keeping creating objects in references to destroy objects on cleaning.
@@ -34,24 +37,24 @@ pub const VM = struct {
     references: std.ArrayList(*Obj),
     strings: Table,
     globals: Table,
-    tracing: bool,
+    frames: [constants.FRAMES_MAX]CallFrame,
+    frame_count: usize,
 
     pub fn new(allocator: Allocator) VM {
         return VM{
             .allocator = allocator,
-            .chunk = null,
-            .ip = null,
             .stack = undefined,
             .stack_top = 0,
             .references = std.ArrayList(*Obj).init(allocator),
             .strings = Table.new(allocator),
             .globals = Table.new(allocator),
-            .tracing = false,
+            .frames = undefined,
+            .frame_count = 0,
         };
     }
 
     pub fn free(self: *VM) void {
-        if (self.has_tracing()) {
+        if (constants.DEBUG_PRINT_INTERNAL_STRINGS) {
             self.strings.dump();
         }
 
@@ -62,35 +65,37 @@ pub const VM = struct {
     }
 
     inline fn current_chunk(self: *VM) *Chunk {
-        return self.chunk.?;
+        return &self.frames[self.frame_count - 1].function.chunk;
     }
 
-    pub fn set_trace(self: *VM, tracing: bool) void {
-        self.tracing = tracing;
-    }
-
-    pub fn has_tracing(self: *VM) bool {
-        return self.tracing;
+    inline fn current_frame(self: *VM) *CallFrame {
+        return &self.frames[self.frame_count - 1];
     }
 
     pub fn interpret(self: *VM, allocator: Allocator, content: []const u8) !InterpretResult {
         var chunk = Chunk.new(allocator);
         defer chunk.deinit();
 
-        const res = try compile(allocator, self, content, &chunk);
-        if (!res) {
+        const function = try compile(allocator, self, content);
+        if (function == null) {
             return InterpretResult.COMPILE_ERROR;
         }
+        defer function.?.destroy();
 
-        self.chunk = &chunk;
-        self.ip = 0;
+        _ = try self.push(Value.obj_val(&function.?.obj));
+
+        const frame = &self.frames[self.frame_count];
+        self.frame_count += 1;
+        frame.function = function.?;
+        frame.ip = 0;
+        frame.slots_idx = self.stack_top;
 
         return try self.run();
     }
 
     pub fn run(self: *VM) !InterpretResult {
         while (true) {
-            if (self.has_tracing()) {
+            if (constants.DEBUG_TRACE_EXECUTION) {
                 if (self.stack_top > 0) {
                     debug.print("{s:32}", .{""});
                     for (0..self.stack_top) |item_idx| {
@@ -100,7 +105,7 @@ pub const VM = struct {
                     }
                     debug.print("\n", .{});
                 }
-                _ = self.current_chunk().dissassemble_instruction(self.ip.?);
+                _ = self.current_chunk().dissassemble_instruction(self.current_frame().ip);
             }
 
             const instruction = self.read_byte();
@@ -180,25 +185,25 @@ pub const VM = struct {
                 },
                 @intFromEnum(OpCode.OP_GET_LOCAL) => {
                     const slot = self.read_byte();
-                    try self.push(self.stack[slot]);
+                    try self.push(self.stack[self.current_frame().slots_idx + slot - 1]);
                 },
                 @intFromEnum(OpCode.OP_SET_LOCAL) => {
                     const slot = self.read_byte();
-                    self.stack[slot] = self.peek(0);
+                    self.stack[self.current_frame().slots_idx + slot - 1] = self.peek(0);
                 },
                 @intFromEnum(OpCode.OP_JUMP) => {
                     const offset = self.read_short();
-                    self.ip.? += offset;
+                    self.current_frame().ip += offset;
                 },
                 @intFromEnum(OpCode.OP_JUMP_IF_FALSE) => {
                     const offset = self.read_short();
                     if (self.peek(0).is_falsey()) {
-                        self.ip.? += offset;
+                        self.current_frame().ip += offset;
                     }
                 },
                 @intFromEnum(OpCode.OP_LOOP) => {
                     const offset = self.read_short();
-                    self.ip.? -= offset;
+                    self.current_frame().ip -= offset;
                 },
                 else => {
                     debug.print("Invalid instruction: {d}\n", .{instruction});
@@ -213,16 +218,16 @@ pub const VM = struct {
     // XXX In the book, we're using a ptr to data directly, to avoid dereferencing to a given offset
     // How to do that in Zig?
     pub fn read_byte(self: *VM) u8 {
-        const ret = self.current_chunk().code[self.ip.?];
-        self.ip.? += 1;
+        const ret = self.current_chunk().code[self.current_frame().ip];
+        self.current_frame().ip += 1;
 
         return ret;
     }
 
     pub fn read_short(self: *VM) u16 {
-        self.ip.? += 2;
+        self.current_frame().ip += 2;
 
-        return (@as(u16, self.current_chunk().code[self.ip.? - 2]) << 8) | (@as(u16, self.current_chunk().code[self.ip.? - 1]));
+        return (@as(u16, self.current_chunk().code[self.current_frame().ip - 2]) << 8) | (@as(u16, self.current_chunk().code[self.current_frame().ip - 1]));
     }
 
     pub fn read_constant(self: *VM) Value {
@@ -287,7 +292,7 @@ pub const VM = struct {
     }
 
     pub fn runtime_error(self: *VM, err_msg: []const u8) void {
-        const instruction = self.ip.?;
+        const instruction = self.current_frame().ip;
         const line = self.current_chunk().lines[instruction];
 
         debug.print("err: {s}\n", .{err_msg});